The reason why rank-checker.online is spamming your website’s Google Analytics data is to get your attention and persuade you to visit the URL in your browser. The website that rank-checker.online forwards to contains paid-services that web masters and anyone who owns a website might essentially find relevant.

Shame on them. If you see you have been hit by rank-checker.online in your analytics the article quoted above sas a fix to prevent their traffic from effecting your rankings.